US5815312AExpiredUtility

Real image type finder

37
Assignee: OLYMPUS OPTICAL COPriority: Mar 14, 1995Filed: Mar 13, 1996Granted: Sep 29, 1998
Est. expiryMar 14, 2015(expired)· nominal 20-yr term from priority
Inventors:Hideyasu Takato
G02B 15/144511
37
PatentIndex Score
6
Cited by
11
References
21
Claims

Abstract

The present invention provides a real image type of zoom finder which, albeit having a zoom ratio as high as at least 3, is short in terms of the total length of an objective, is well corrected in terms of aberrations and ensures good viewing, and which comprises, in order from the object side, an objective having a positive refracting power, an optical system for inverting the upper, lower, left and right parts of an image formed by said objective, and an eyepiece having a positive refracting power, wherein the objective consists essentially of a first lens group G 1 having a negative refracting power, a second lens group G 2 having a positive refracting power, a third lens group G 3 having a negative refracting power and a fourth lens group G 4 having a positive refracting power, each consisting of one lens or the second lens group G 2 consisting of two lenses, and conforms to the following conditional inequality (1): 1.35<|f.sub.1 /f.sub.2 |×m.sub.T <2.4 (1) where: f 1 is the focal length of the first lens group, f 2 is the focal length of the second lens group, and m T is the magnification of the finder at the telephoto end.

Claims

exact text as granted — not AI-modified
What we claim is: 
     
       1. A real image type of zoom finder comprising, in order from the object side, an objective having a positive refracting power, an optical system for inverting the upper, lower, left and right parts of an image formed by said objective, and an eyepiece having a positive refracting power, wherein said objective consists essentially of a first lens group having a negative refracting power, a second lens group having a positive refracting power, a third lens group having a negative refracting power and a fourth lens group having a positive refracting power, separations between said respective lens groups being varied for zooming, and conforms to the following conditional inequality (1):   1.35<|f.sub.1 /f.sub.2 |×m.sub.T <2.4(1)     where:   f 1  is a focal length of the first lens group,   f 2  is a focal length of the second lens group, and   m T  is a magnification of the finder at the telephoto end.   
     
     
       2. A real image type of zoom finder comprising, in order from the object side, an objective having a positive refracting power, an optical system for inverting the upper, lower, left and right parts of an image formed by said objective, and an eyepiece having a positive refracting power, wherein: said objective consists essentially of a first lens group having a negative refracting power, a second lens group having a positive refracting power, a third lens group having a negative refracting power and a fourth lens group having a positive refracting power, each of said respective lens groups consisting of one lens and separations between said respective lens groups being varied for zooming.   
     
     
       3. A real image type of zoom finder comprising, in order from object side, an objective having a positive refracting power, an optical system for inverting upper, lower, left and right parts of an image formed by said objective, and an eyepiece having a positive refracting power, wherein: said objective consists essentially of a first lens group consisting of a single lens having a negative refracting power, a second lens group consisting of two lenses and having a positive refracting power as a whole, a third lens group having a negative refracting power and a fourth lens group having a positive refracting power, separations between said respective lens groups being varied for zooming.   
     
     
       4. The real image type of zoom finder according to claim 1, wherein each of the lens groups forming said objective consists essentially of up to two lenses. 
     
     
       5. The real image type of zoom finder according to claim 1, wherein the first lens group forming part of said objective has at least one aspheric surface. 
     
     
       6. The real image type of zoom finder according to claim 1, wherein the second lens group forming part of said objective has at least one aspheric surface. 
     
     
       7. The real image type of zoom finder according to claim 1, wherein said objective conforms to the following conditional inequality (2):   0.2<f.sub.2 /f.sub.T <0.64                                 (2)     is focal length of the objective at the telephoto end.   
     
     
       8. The real image type of zoom lens according to claim 1, wherein the second and third lens groups forming part of said objective are movable on the optical axis for zooming. 
     
     
       9. The real image type of zoom lens according to claim 1, wherein said objective conforms to the following conditional inequality (3):   0<|f.sub.3 /f.sub.T |<1                  (3)     where f 3  is th focal length of the third lens group and f T  is a focal length of the objective at the telephoto end.   
     
     
       10. The real image type of zoom finder according to claim 1, wherein each of the respective lens groups forming said objective consists essentially of one lens. 
     
     
       11. The real image type of zoom finder according to claim 1, wherein the first lens group forming part of said objective consists essentially of one single lens and said second lens group consists essentially of two lenses. 
     
     
       12. The real image type of zoom finder according to claim 1 or 2, wherein at least three lens groups of the four lens groups forming said objective are movable along the optical axis for zooming. 
     
     
       13. The real image type of zoom finder according to claim 1, wherein said first lens group consists essentially of two lenses, and said second, third and fourth lens groups each consists essentially of one lens. 
     
     
       14. The real image type of zoom finder according to claim 1, wherein the first lens group forming part of said objective consists essentially of one single lens and said second lens group consists essentially of two lenses. 
     
     
       15. The real image type of zoom finder according to claim 2 or 3, wherein the first lens group forming part of said objective has at least one aspheric surface. 
     
     
       16. The real image type of zoom finder according to claim 2 or 3, wherein the second lens group forming part of said objective has at least one aspheric surface. 
     
     
       17. The real image type of zoom finder according to claim 4 or 3, wherein said objective conforms to the following conditional inequality (2):   0.2<f.sub.2 /f.sub.T <0.64                                 (2)     where f 2  is a focal length of the second lens group, and f T  is a focal length of the objective at the telephoto end.   
     
     
       18. The real image type of zoom lens according to claim 2 or 3, wherein the second and third lens groups forming part of said objective are movable on the optical axis for zooming. 
     
     
       19. The real image type of zoom lens according to claim 4 or 3, wherein said objective conforms to the following conditional inequality (3):   0<|f.sub.3 /f.sub.T |<1                  (3)     where f 3  is a focal length of the third lens group and f T  is a focal length of the objective at the telephoto end.   
     
     
       20. A real image type of zoom finder comprising, in order from the object side, an objective having a positive refracting power, an optical system for inverting upper, lower, left and right parts of an image formed by said objective, and an eyepiece having a positive refracting power, wherein: said objective consists essentially of a first lens group having a negative refracting power, a second lens group having a positive refracting power, a third lens group having a negative refracting power and a fourth lens group having a positive refracting power, at least three lens groups of said four lens groups being movable during zooming,   wherein said objective conforms to the following conditional inequality (2):   0.2<f.sub.2 /f.sub.T <0.64                                 (2)     where f 2  is a focal length of the second lens group, and f T  is a focal length of the objective at the telephoto end.     
     
     
       21. A real image type of zoom finder comprising, in order from the object side, an objective having a positive refracting power, an optical system for inverting upper, lower, left and right parts of an image formed by said objective, and an eyepiece having a positive refracting power, wherein: said objective consists essentially of a first lens group having a negative refracting power, a second lens group having a positive refracting power, a third lens group having a negative refracting power and a fourth lens group having a positive refracting power, at least three lens groups of said four lens groups being movable during zooming,   wherein said objective conforms to the following conditional inequality (3):   0<|f.sub.3 /f.sub.T |<1                  (3)     where f 3  is a focal length of the third lens group.

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